Internal combustion engines generate motive power (e.g., mechanical work) by the burning of fossil fuels within combustion chambers of the engine. During combustion, the hot exhaust gasses produced are used to drive a piston, and/or to carry out other work in the vehicle, as they expand. The hot exhaust gasses then travel through an exhaust system of the vehicle before exiting into the atmosphere. A byproduct of combusting the fossil fuels is heat. Only a small fraction of the energy located in fossil fuel chemical bonds is used to propel the motor vehicle forwards, and much of the energy is lost to the environment in the form of unusable, entropic heat. The combustion of fossil fuels within the combustion chambers happens in a repetitious and cyclic manner, and may therefore be considered a type of thermodynamic cycle. By recovering and subsequently utilizing the heat produced during the step or steps of the combustion cycle when heat is produced as a byproduct (e.g., combustion), it may be possible to recover thermal energy from exhaust gases in the internal combustion engine in order to enhance fuel economy.
As one example, a method for recovering and utilizing waste thermal energy from exhaust gases in an internal combustion engine may include utilizing a bottoming cycle, such as a Rankine Cycle, to generate mechanical or electrical power, referred to herein as work, from the entropic heat of the exhaust gasses generated during combustion. Specifically, the waste heat of the exhaust gasses may be transferred to a working fluid to generate a steam that may be used to generate work within the motor vehicle, thereby enhancing fuel economy. The working fluid steam is then condensed into liquid form to reenter and begin the thermodynamic Rankine cycle anew. One example approach is shown by Gleich et al. in DE Patent Application No. 201210015927. Therein, Gleich discloses a waste-gas heat exchanger installed in a combustion cylinder liner, wherein the liner contains a working fluid that may be converted to steam to generate work in the vehicle, in a Rankine Cycle style.
However, the inventors herein have recognized potential issues with such systems. As one example, cylinders have varying temperatures from one another depending on operating conditions of the vehicle, and cooling cylinders homogenously via the same amount of working fluid in each cylinder liner when one or more cylinders are already at a relatively cool temperature, may have negative effects on combustion efficacy and fuel economy.
In one example, the issues described above may be addressed by a method comprising individually injecting fluid into a plurality of tubes of a tube array, where each tube of the plurality of tubes passes through a combustion chamber of a corresponding engine cylinder in an area of a head of the engine cylinder, based on a temperature of the engine cylinder; and recovering heat energy from the injected fluid after it passes through each tube. In this way, the fluid, which herein may be referred to as a working fluid, may be converted from a liquid to gaseous state by the waste heat in exhaust gasses in order to do additional work in the motor vehicle, in a fashion tailored to each individual combustion cylinder, thereby increasing combustion efficiency and fuel economy.
As one example, a controller may be used to monitor the temperature of each combustion cylinder and the amount and/or timing of the fluid injected into the corresponding engine cylinder may be modified so that the temperature of the cylinder is kept within a threshold combustion range. For example, if an engine cylinder is running hotter than its counterparts, more fluid may be injected into the tubing passing through that cylinder to help cool it down. Alternatively, if a particular engine cylinder is running below a temperature threshold, less or no fluid may be injected into the tubing passing through that cylinder in order to increase the temperature of the cylinder and put it on par with the other cylinders of the engine.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.